Australian native flower colours: Does nectar reward drive bee pollinator flower preferences?

Abstract

Colour is an important signal that flowering plants use to attract insect pollinators like bees. Previous research in Germany has shown that nectar volume is higher for flower colours that are innately preferred by European bees, suggesting an important link between colour signals, bee preferences and floral rewards. In Australia, flower colour signals have evolved in parallel to the Northern hemisphere to enable easy discrimination and detection by the phylogenetically ancient trichromatic visual system of bees, and native Australian bees also possess similar innate colour preferences to European bees. We measured 59 spectral signatures from flowers present at two preserved native habitats in South Eastern Australia and tested whether there were any significant differences in the frequency of flowers presenting higher nectar rewards depending upon the colour category of the flower signals, as perceived by bees. We also tested if there was a significant correlation between chromatic contrast and the frequency of flowers presenting higher nectar rewards. For the entire sample, and for subsets excluding species in the Asteraceae and Orchidaceae, we found no significant difference among colour categories in the frequency of high nectar reward. This suggests that whilst such relationships between flower colour signals and nectar volume rewards have been observed at a field site in Germany, the effect is likely to be specific at a community level rather than a broad general principle that has resulted in the common signalling of bee flower colours around the world.

Do visual traits honestly signal floral rewards at community level?

“…To our knowledge, the relationship between nectar offer and colour as perceived by bees has been explored only in five communities. In three of these (including the present one), some degree of association was found between both parameters (Giurfa et al, 1995;Kantsa et al, 2017), whereas no relationship was detected in the other two (Shrestha et al, 2020). We do not know any other study, apart from the present one, which explores this kind of relationships for pollen offer at community level.…”

“…The association between rewards and floral cues mediates pollinator services at community level (Herrera, 2020). However, there has been scant research on this relationship at the aforementioned level Kantsa et al, 2017;Shrestha et al, 2020) and the offer both of nectar and of pollen has never been studied. In the Mediterranean Basin, most species flower in the spring, coinciding with maximum richness of insect taxa (Herrera, 1988).…”

Floral Color Diversity: How Are Signals Shaped by Elevational Gradient on the Tropical–Subtropical Mountainous Island of Taiwan?

“…and Bombus sp., as well as phylogenetically separated bee species like the stingless bee Tetragonula carbonaria (Figure 7). Interestingly, such color preferences have been observed to be biologically relevant considering the foraging decisions of naïve bees visiting real flowers (Dyer et al, 2019), providing a plausible explanation for how insect preferences do influence plant fitness and flower color signaling (Giurfa et al, 1995;Shrestha et al, 2020). In addition, floral color loci in the three altitudinal regions of TW we tested consistently and predominantly fall in the sector of bee color space preferred by bees (Figure 7).…”

Fragmentary Blue: Resolving the Rarity Paradox in Flower Colors

“…In Germany, it was reported that blue flowers more frequently presented higher reward (Giurfa et al, 1995) than alternative flower colors. However, recent work in Australia reports no evidence that any particular color among bee-pollinated flowers was associated with higher nectar rewards (Shrestha et al, 2020), and so currently there is no conclusive evidence of higher rewards being associated with blue flowers. According to Rodríguez-Gironés and Santamaría 2004, interactions among pollinators of different types might interfere with the expression of a color preference.…”